Goal

• The `–drive stats-intervals` option enables time-based I/O statistics, including queue depth. libvirt needs `–blockdev` to support the `stats-intervals` parameter that is already available with the legacy `–drive` option. This is because libvirt uses the modern `–blockdev` syntax.
• A QMP command interface (similar to `block_set_io_throttle`) that allows enabling/disabling stats-intervals at runtime is also needed. Although this may not be used by CNV right away, it will future-proof the interface in case there is a need to collect stats on for a window of time.

Acceptance criteria

• At least the JSON `–blockdev` syntax must support stats-intervals: `–blockdev {..., 'stats-intervals': [1]}

  `

• Optionally, the non-JSON syntax might be able to support `–blockdev ...,stats-intervals.0=1`. At the time of writing I don't remember the limitations of the non-JSON parser, this needs to be investigated.
• A QMP command interface toggles stats-intervals and the stats can be seen updating (or not) using the query-blockstats QMP command.